ADU rules in Arlington

Arlington's ADU analog is the 'secondary living unit': a second single-family living unit on the same lot with its own living/sleeping, cooking, and sanitation, which may be detached. Per use Table 3.3-1 it is permitted with supplemental standards (P*) in the RE, RS-20, RS-15, and VG districts, but needs a Specific Use Permit in RS-7.2, RS-5, and RM-12, the city's most common single-family districts, and is not allowed in RMF-22. The major catch is occupancy: the unit is only for family members or relatives and cannot be rented or leased.

The same secondary living unit use covers attached units, with the same district split as detached; if attached it must have its own entrance not connected to the primary structure. Two narrower attached options exist: caretaker's quarters (inside or attached by a common wall, allowed in RE and VG among residential districts, with recorded use covenants required before a building permit) and garage apartments (a dwelling unit built as part of a private garage, allowed only in RM-12, RMF-22, DB, NMU, and RMU, where it counts toward density).

The practical size limit is the one-bedroom, one-kitchen, one-bathroom rule plus the district envelope (RS-7.2, for example, allows 40 ft height and 50 percent lot coverage). The unit counts toward the accessory building cap of 3 buildings on lots under 1 acre (5 on 1 acre and larger), detached accessory buildings of 550 sq ft or more trigger the primary-structure exterior material standards, and an accessory building's roof may not exceed the primary structure's height.

Neither the UDC's accessory dwelling provisions nor the Short-Term Rental chapter contains an owner-occupancy requirement; a full-text search of both found none. Arlington instead restricts who may occupy the unit: a secondary living unit is only for family members or relatives and cannot be leased, and caretaker's quarters require the owner to record restrictive covenants limiting the unit's use before a building permit issues (the covenant contents are not spelled out in the UDC, so verify current practice with Planning and Development Services).

Homeowners adding a secondary living unit do not have to add any parking, a garage, or a carport for the unit. Caretaker's quarters have no separate parking line item in Table 5.4-1.

In RE, RS-20, RS-15, and VG, a secondary living unit is a permitted accessory use built under a standard building permit subject to the §3.3.6.L standards. In RS-7.2 and RS-5, Arlington's workhorse single-family districts (7,200 and 5,000 sq ft minimum lots), and in RM-12, it requires a Specific Use Permit, adopted by ordinance after a Planning and Zoning Commission public hearing and City Council approval. It is not allowed at all in RMF-22.

This is the defining feature of Arlington's rules: the code deliberately prevents accessory units from becoming ordinary rental income units. Long-term leasing is prohibited by definition, and short-term rental of any dwelling requires a permit that is geographically unavailable in single-family neighborhoods outside the entertainment-district STR Zone. Operating an unpermitted STR is unlawful, with fines per the ordinance's enforcement provisions.